Magnetic field sensor with increased snr

ABSTRACT

Various means for improvement in signal-to-noise ratio (SNR) for a magnetic field sensor are disclosed for low power and high resolution magnetic sensing. The improvements may be done by reducing parasitic effects, increasing sense element packing density, interleaving a Z-axis layout to reduce a subtractive effect, and optimizing an alignment between a Z-axis sense element and a flux guide, etc.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalApplication No. 62/156,013, filed May 1, 2015, and U.S. ProvisionalApplication No. 62/154,210, filed Apr. 29, 2015, the entire contents ofwhich are herein incorporated by reference.

TECHNICAL FIELD

The present inventions relate generally to the field of magnetic fieldsensors and more particularly to methods of increasing signal-to-noiseratio (SNR) of magnetic field sensors.

BACKGROUND OF THE INVENTION

Magnetic field sensors have been commonly used in various electronicdevices, such as computers, laptops, media players, smart phones, etc.There are several techniques/devices that can be used for detecting amagnetic field. Tunneling Magnetoresistance (TMR) is a promisingmagnetic sensing technology for handset applications due to itsadvantages in sensitivity, power, and process cost compared with othermagnetic sensors. Another closely related technology in magnetic fieldsensing is Giant Magnetoresistance (GMR), and many of the disclosedembodiments apply equally well to GMR based sensing technologies.

A TMR element is composed of two ferromagnetic layers separated by anon-magnetic, insulating tunnel barrier. One layer has a magnetizationdirection that is “free” to rotate in a magnetic field. The other layer(reference layer) has a “fixed,” reference magnetization that does notrotate when in a magnetic field of moderate to low strength that is ofsensing interest. If the magnetization directions of the two layers areparallel to each other, the electrical resistance of the tunnel barrieris low. Conversely, when the magnetization directions are anti-parallel,the resistance is high. A magnetic field sensor based on TMR thereforeconverts magnetic field into electrical signal by a change in electricalresistance due to the changing angle of the magnetization direction ofthe magnetic free layer relative to the reference magnetization of thefixed layer in response to the field.

The performance of a magnetic sensor may be defined by itssignal-to-noise ratio (SNR). Magnetic sensors with high SNR need highpower for operation to achieve desired output signal quality andgenerally are not applicable to situations where high precision magneticfield measurement is required.

Therefore, it would be desirable to have a system, device, and method toeffectively increase a signal-to-noise ratio (SNR) of magnetic fieldsensors for lower power and high resolution magnetic sensing.

SUMMARY OF THE INVENTION

Certain embodiments of the inventions provide for systems, devices, andmethods to effectively increase a SNR of a TMR magnetic field sensor forlow power, high resolution magnetic sensing.

According to various embodiments of the inventions, various means forimprovement in a SNR for a TMR field sensor are disclosed. Theimprovement may be done by reducing parasitic effects, increasing senseelement packing density, interleaving a Z-axis layout to reduce asubtractive effect, and optimizing an alignment between a Z-axis senseelement and a flux guide, etc.

In certain embodiments, a magnetic sensor is built with a Wheatstonebridge circuit with each leg comprising an identical number of senseelements. Such a design may avoid a differential response to in-planefields since all elements respond in the same way. Moreover, an evennumber of sense elements, preferably 4 sense elements, per metalmagnetic tunnel (MMT) is utilized for a balanced sense current flow(e.g., equal SNR weighting for each sense element), and the sensecurrent flows vertically through the magnetic tunnel junction (MTJ)sense elements and perpendicular to an MMT orientation, whichinterconnects adjacent sense elements for minimal resistive losses.

In certain embodiments, for Z-axis magnetic sensing, a Z-axis layout isinterleaved to take advantage of both sides of a flux guide. Preferably,dual flux guides are utilized for an optimal trench width whilemaintaining pitch and spacing constraints of a reference layer within aTMR sense element. Sense elements may also be used on both sides of aflux guide to eliminate the subtractive effect that is present when theinactive ferromagnetic side of one trench is close enough to interactwith a side of an adjacent sense element column. Adjacent sense elementsmay be arranged to have an opposite response to an out-of-plane field,and hence, Z-axis sensor legs become interleaved with one another toallow for denser packing, a relatively higher sense element occupationarea, and a relatively higher SNR without impacting sensitivity due tothe aforementioned subtractive effect.

In certain embodiments, built-in reset lines within the TMR sensor arerouted at a 45 degree cross angle to the easy (long) axis of a magneticsense element to lower a switching threshold by about a factor of two,as compared to a 90 degree cross angle reset line routing. Furthermore,the reset lines within the TMR sensor may be utilized in a bipolarchopping method in combination with the aforementioned means to furtherlower sensor output signal noise.

While the present inventions are discussed below using TMR magneticfields sensors having TMR elements, all aspects of the inventions willdirectly apply to devices based on giant magnetoresistance (GMR)technology as well. The inventions disclosed here also apply to anymagnetic sensing technology that utilizes soft-magnetic films forsensing magnetic fields, such as, for example, anisotropicmagnetoresistance (AMR), Fluxgate, and Hall sensors with a fluxconcentrator. For simplicity and clarity, the inventions will bedescribed in more detail below using TMR technology as an example.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made to exemplary embodiments of the presentinventions that are illustrated in the accompanying figures. Thosefigures are intended to be illustrative, rather than limiting. Althoughthe present inventions are generally described in the context of thoseembodiments, it is not intended by so doing to limit the scope of thepresent inventions to the particular features of the embodimentsdepicted and described.

FIG. 1 depicts a cross-section view of a single TMR element cell,according to various embodiments of the inventions.

FIG. 2 depicts an exemplary structure overview of a TMR transducer leg,with multiple element cells, according to various embodiments of theinventions.

FIG. 3 depicts an exemplary structure overview of a Z-axis TMRtransducer leg, with multiple Z-axis TMR element cells, according tovarious embodiments of the inventions.

FIG. 4 depicts a prior art cross-section structure overview of typicalinterconnections of X/Y-axis TMR element cells.

FIG. 5 depicts an exemplary cross-section structure overview ofinterconnections of X/Y-axis TMR element cells, according to variousembodiments of the inventions.

FIG. 6 depicts a prior art cross-section structure overview of typicalinterconnections of Z-axis TMR element cells.

FIG. 7 depicts an exemplary cross-section structure overview ofinterconnections of Z-axis TMR element cells according to variousembodiments of the inventions.

FIGS. 8A-8C show cross-section views of Z-axis TMR sense element cellsand flux guides according to various embodiments of the inventions.

FIG. 9 depicts an exemplary structure overview of a TMR magnetic fieldsensor comprising a bridge circuit with multiple TMR transducer legsaccording to various embodiments of the inventions.

FIGS. 10A-10B depict exemplary diagrams of bridge circuit formeasurement of X- or Y-axes of a magnetic field according to variousembodiments of the inventions.

FIGS. 11A-11B depict exemplary diagrams of bridge circuits formeasurement of a Z-axis magnetic field according to various embodimentsof the inventions.

FIG. 12 depicts an exemplary structure diagram of an array of X/Y-axisTMR element cells according to various embodiments of the inventions.

FIG. 13 depicts a second exemplary structure diagram of an array ofX/Y-axis TMR element cells according to various embodiments of theinventions.

FIG. 14 depicts an exemplary structure diagram of an array of Z-axis TMRelement cells according to various embodiments of the inventions.

FIGS. 15A-15C depict exemplary schematic diagrams of an array of Z-axisTMR element cells according to various embodiments of the inventions.

FIG. 16 depicts an exemplary schematic diagram of an array of Z-axis TMRelement cells, with 45 degree reset current lines, according to variousembodiments of the inventions.

One skilled in the art will recognize that various implementations andembodiments of the inventions may be practiced in accordance with thespecification. All of these implementations and embodiments are intendedto be included within the scope of the inventions.

As used herein, the terms “comprises,” “comprising,” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises a list ofelements does not include only those elements, but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. The term “exemplary” is used in the sense of“example,” rather than “ideal.”

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, for the purpose of explanation, specificdetails are set forth in order to provide an understanding of thepresent inventions. The present inventions may, however, be practicedwithout some or all of these details. The embodiments of the presentinventions described below may be incorporated into a number ofdifferent electrical components, circuits, devices, and systems.Structures and devices shown in block diagram are illustrative ofexemplary embodiments of the present inventions and are not to be usedas a pretext by which to obscure broad teachings of the presentinventions. Connections between components within the figures are notintended to be limited to direct connections. Rather, connectionsbetween components may be modified, re-formatted, rerouted, or otherwisechanged by intermediary components.

When the specification makes reference to “one embodiment” or to “anembodiment”, it is intended to mean that a particular feature,structure, characteristic, or function described in connection with theembodiment being discussed is included in at least one contemplatedembodiment of the present inventions. Thus, the appearance of thephrase, “in one embodiment,” in different places in the specificationdoes not constitute a plurality of references to a single embodiment ofthe present inventions.

Various embodiments of the inventions are used for systems, devices, andmethods to effectively increase the SNR of a TMR magnetic field sensorand maintain desired measurement sensitivity. The TMR magnetic fieldsensors, and the TMR element(s) therein, may be integrated on a singlecomponent or contain discrete components. Furthermore, embodiments ofthe inventions are applicable to a diverse set of techniques andmethods.

As mentioned above, the magnetic field sensors as claimed herein maymean one or more of TMR magnetic fields sensors, GMR magnetic fieldsensors, AMR magnetic field sensors, Fluxgate magnetic field sensors,and/or Hall magnetic field sensors with a flux concentrator. Further,magnetoresistance sense elements as claimed herein may mean one or moreof TMR elements, GMR elements, AMR elements, Fluxgate elements, and/orHall elements with flux concentrators.

FIG. 1 illustrates a cross-section view of a single TMR element cell100, according to various embodiments of the inventions. The TMR elementcell 100 is composed of a first patterned ferromagnetic layer 112 and asecond ferromagnetic layer 114 separated by a non-magnetic, insulatingtunnel barrier 116 (also called a tunnel junction (TJ)). In oneembodiment, the first layer 112 (also referred as sense element) has amagnetization direction 132 that is free to rotate in a magnetic field.The second layer 114 (reference layer) has a fixed referencemagnetization direction 134 that does not rotate when in a magneticfield. If the magnetization directions of the two layers are parallel toeach other, the electrical resistance of the tunnel barrier 116 isrelatively low. Conversely, when the magnetization directions areantiparallel, the resistance is relatively higher.

The TMR element cell 100 therefore converts a magnetic field intoelectrical signal by changing the electrical resistance due to achanging angle of the magnetization direction 132 of the magnetic freelayer relative to the reference magnetization direction 134 of the fixedlayer in response to the field. The ferromagnetic layers 112 and 114 maybe formed from any suitable ferromagnetic material, such as Ni, Fe, Co,or their alloys. The insulating tunnel barrier 116 may be composed ofinsulator materials such as AlOx, MgOx, ZrOx, TiOx, HfOx, or anycombinations thereof.

Typically, the first ferromagnetic layer 112 is connected to a firstconductive line 124 by a first contact 122, and the second ferromagneticlayer 114 is connected to a second conductive line 128 by a secondcontact 126, which may contact from above as well as below the secondferromagnetic layer 114. The second conductive line 128 may also bereferred as metal magnetic tunnel (MMT) layer. In one embodiment, thefirst conductive line 124 and the second conductive line 128 may connectto other TMR element cells 100 to form a TMR element cell array.

In one embodiment, the TMR element cell 100 comprises a built-in currentline 410 located, disposed, or deposited adjacent to the secondferromagnetic layer 114 to carry a reset current. The current line 410of one TMR element cell 100 may be coupled to current lines of multipleother TMR element cells. In another embodiment, the TMR element cell 100also comprises a second built-in current line 420 located, disposed, ordeposited adjacent to the first ferromagnetic layer 112. The firstferromagnetic layer 112 is patterned into a shape that has a long axisand a short axis. In a zero magnetic field, the magnetization directionof the first ferromagnetic layer 112 lies along the long axis of theelement 100, and can be directed in either of the two directions alongthis axis. By applying a reset current signal to the current line 410and/or the current line 420, an induced magnetic field is generated inan ambient area surrounding the respective current line 410/420. Sincethe first layer 112 has a magnetization direction 132 that is free torotate and switch, the magnetization direction 132 will switch to bealong the direction projected on its axis by the induced magnetic field.As an exemplary illustration in FIG. 1, when the current in the currentline 410 has a direction pointing outward (relative to the page) and thecurrent in the current line 420 has a direction pointing inward(relative to the page), the magnetization direction 132 points leftward,which is has a component that is negatively aligned to the referencemagnetization direction 134, and will switch the magnetization direction132 of the free layer to the left; when the current in the current line410 has a direction pointing inward and/or the current in the currentline 420 has a direction pointing outward, the magnetization direction132 points rightward, which has a component that is positively alignedto the reference magnetization direction 134, and will switch themagnetization direction 132 of the free layer to the right.

In one embodiment, the TMR element cell 100 comprises at least onebuilt-in flux guide (not shown in FIG. 1 for figure clarity) for Z-axismagnetic field sensing. The flux guide 118 is shown in FIGS. 3, 6, and7, and will be described below.

FIG. 2 depicts an exemplary structure overview of a TMR transducer leg210, with multiple element cells 100, according to various embodimentsof the inventions. The TMR transducer leg 210 comprises an array ofmultiple active sense element cells 100 a-100 d, preferably arranged ina matrix layout. In one embodiment, each TMR transducer leg 210comprises an array of 24×24 sense element cells 100, which isapproximately 100×100 um² in size overall. The current flow in currentlines 410 a and 410 b of each sense element cell 100 may or may not bethe same direction. It is understood that the structure shown in FIG. 2is only for a general illustration purpose. Various sense elementcoupling patterns within the array may be implemented other than thepattern disclosed in FIG. 2. In one embodiment, a sense element cell(e.g., cells 100 a, 100 c) may have the opposite current directionrelative to a current line of a neighbor sense element cell (e.g., cells100 b and 100 d). For the highest signal-to-noise ratio in a given chiparea (the densest packing of sense element cells), multiple TMR elementcells 100 may share a common reference layer (such as, for example, acommon second ferromagnetic layer 114). In one embodiment, four senseelement cells may share the common reference layer for a balanced sensecurrent flow, where each TMR element cell has equal SNR weighting. Sucha configuration is shown in the circled region labeled One MMT″ in FIG.12.

FIG. 3 depicts an exemplary structure overview of a Z-axis TMRtransducer leg 310, with multiple element cells 311, according tovarious embodiments of the inventions. Each Z-axis TMR transducer leg310 comprises an array of multiple active Z-axis TMR element cells 311a-311 d, preferably arranged in a matrix layout. In one embodiment, eachZ-axis TMR transducer leg 310 comprises an array of 60×40 Z-axis senseelements cells 311, which is approximately 150×200 um² in size overall.The Z-axis TMR element cells 311 have similar structure as the TMRelement cell 100 shown in FIG. 1, except that a Z-axis TMR element cell311 also comprises at least one flux guide 118. While flux guides 118are located, disposed, or deposited on the right side and underneath afirst ferromagnetic layer 312 of the Z-axis sense elements cells 311(equivalent to the first ferromagnetic layer 112 shown in FIGS. 1 and 2)as illustrated in FIG. 3, it is understood that flux guides 118 may belocated, disposed, or deposited on the left side and/or above the firstferromagnetic layer 312 of the Z-axis sense elements cells 311. TheZ-axis sensitivity may be doubled by locating, disposing, or depositingflux guides 118 on opposing sides and planes of the sense element cell311; i.e., right side, underneath and left side, above. The current flowin current lines 410 of each Z-axis TMR element cell 311 may or may notbe the same direction. In one embodiment, a Z-axis sense element cell311 a, 311 c may have the opposite current direction relative to thecurrent line of a neighbor Z-axis sense element 311 b, 311 d.

FIG. 4 depicts a prior art cross-section structure overview of typicalinterconnections of X/Y-axis TMR element cells. Each secondferromagnetic layer 114 (MMT) couples to only one first ferromagneticlayer 112. The TJ 116 is not shown explicitly in FIGS. 4-7. Therefore, aseparate via 142 on the second ferromagnetic layer 114 (MMT) has to beused for electrical connection between TMR sense element cells.

FIG. 5 depicts an exemplary cross-section structure overview ofinterconnections of X/Y-axis TMR element cells according to variousembodiments of the inventions. Compared to FIG. 4, a secondferromagnetic layer 114 (MMT) and an upper conductor layer 124 couple tomultiple first ferromagnetic layers 112, and are used directly as aconnection conductor for series coupling between TMR sense elementswithout additional vias or interconnection length. By doing so, theelectrical coupling path is lowered significantly, as are the parasiticeffects from the coupling path. In a preferred embodiment, each secondferromagnetic layer 114 (MMT) couples to four first ferromagnetic layers112. In one embodiment, all sense element cells are arranged in a singlerow or column on the MMT (see, e.g., FIG. 12). Moreover, a sense currentflows vertically through the MTJ sense element cells and perpendicularto an MMT orientation, which interconnects adjacent sense element cellsfor minimal resistive losses.

FIG. 6 depicts a prior art cross-section structure overview of typicalinterconnections of Z-axis TMR element cells. Similar to FIG. 4, eachsecond ferromagnetic layer 114 (MMT) couples to only one firstferromagnetic layer 112. Therefore, a separate via 142 on the secondferromagnetic layer 114 (MMT) has to be used for electrical connectionconnections between sense element cells.

FIG. 7 depicts an exemplary cross-section structure overview ofinterconnections of Z-axis TMR element cells according to variousembodiments of the inventions. Compared to FIG. 6, the secondferromagnetic layer 114 (MMT) couples to multiple first ferromagneticlayers 112, and is used directly as a connection conductor for seriescoupling between sense element cells. By doing so, the electricalcoupling path is lowered significantly, as are the parasitic effectsfrom the coupling path. In a preferred embodiment, each secondferromagnetic layer 114 (MMT) couples to two first ferromagnetic layers112. Such an arrangement would be beneficial for a balanced sensecurrent flow because each sense element cell has equal SNR weighting.

FIGS. 8A-8C show a comparison between cross-section views of typicalZ-axis TMR element cells and Z-axis TMR element cells according tovarious embodiments of the inventions. The cross-section views extend tomultiple TMR element cells. For clarity, some components such as thesecond ferromagnetic layers 114, the insulating tunnel barriers 116,etc., are not shown in FIGS. 8A-8C. The flux guides 118 are high aspectratio vertical bars made from a high permeability magnetic material withends terminating in close proximity to opposed edges of the TMR senseelements (i.e., the first ferromagnetic layers 112). A flux guide 118captures magnetic flux from an applied field oriented in the Z-axisdirection, and bends the field lines to have a horizontal component nearthe ends of the flux guide 118. The first ferromagnetic layer 112responds only to in-plane magnetic fields, and therefore, does notrespond to a Z-axis magnetic field directly. The flux guide 118 bendsthe Z-axis magnetic field into a horizontal direction such that thefirst ferromagnetic layer 112 may respond accordingly.

FIG. 8A depicts a cross-section view of TMR sense element cells and fluxguides for two adjacent typical Z-axis TMR element cells. Each TMR senseelement cell only comprises one flux guide 118, which is placedasymmetrically between two neighbor sense element cells (i.e., the firstferromagnetic layers 112). Because of the asymmetry, a subtractiveeffect arises between the flux guide 118 and the farther sense elementcell (this interaction is depicted with the (-) symbol in FIG. 8A. Whilesmaller in magnitude due to the distance from the flux guide edge, theZ-axis field conversion from the farther sense element cell (in-planecomponent) is opposite to and subtracts from the in-plane component ofthe Z-axis field conversion for the neighbor sense element cell.

FIGS. 8B and 8C show cross-section views of TMR sense element cells andflux guides for two different types of Z-axis TMR element cellsaccording to various embodiments of the inventions. In FIG. 8B, dualflux guide trenches 118 a and 118 b instead of a single wide flux guide118 c (FIG. 8C) are utilized. The dual flux guide trenches 118 a and 118b are located, disposed, or deposited symmetrically between neighborsense element cells (i.e., first ferromagnetic layers 112). Furthermore,the dual flux guide trenches 118 a and 118 b (with the gap between thedual flux guide trenches) cover the whole space between the neighborsense element cells widthwise. Such an arrangement decouplesrequirements on sense element pitch, MMT spacing, and trench width,allowing for optimal use of all. In FIG. 8C, a wide trench flux guide118 c is located, disposed, or deposited symmetrically between theneighbor sense element cells (i.e., first ferromagnetic layers 112), andcovers the whole space between the neighbor sense element cellswidthwise. Although the dual flux guide trenches 118 a and 118 b andwide trench flux guide 118 c are shown below the first ferromagneticlayers 112 in FIGS. 8B and 8C, the dual flux guide trenches 118 a and118 b and wide trench flux guide 118 c may also be located, disposed, ordeposited above the first ferromagnetic layers 112. In one embodiment,the flux guides shown in FIGS. 8A-8C are fabricated with a thinferromagnetic material layer 119 coated on both sides of the trench torespond to a Z-axis magnetic field.

FIG. 9 shows a schematic diagram of a TMR magnetic field sensor 200according to various embodiments of the inventions. The magnetic fieldsensor 200 comprises a first bridge circuit 220 powered by a voltagesource 300 connected via a voltage source connection 300 a, and a secondcircuit 400 powered by an optional reset field source 500, which may bea current source connected via a reset field source connection 500 a.The first bridge circuit 220 comprises a plurality of TMR transducerlegs 210 (or a plurality of Z-axis TMR transducer legs 310). The bridgecircuit 220 may be a half bridge circuit, a full bridge circuit, or anycombinations thereof. In one embodiment, the bridge circuit 220 is aWheatstone bridge circuit having two circuit branches with a bridgeoutput signal 260 between the two branches at some intermediate pointalong the branches. The TMR transducer leg 210 (or the Z-axis TMRtransducer leg 310) electrically functions as a resistor with itsresistance value variable in response to internal and external magneticfields. The current line 410 of each TMR element cell 100 (or Z-axis TMRelement cell 311) routes together with various routing patterns to formthe second circuit 400.

FIGS. 10A and 10B depict exemplary diagrams of bridge circuits formeasurement of X- or Y-axes of a magnetic field, with the current linesenergized, according to various embodiments of the inventions. When areset current is applied to the current line 410 of FIG. 1, for example,a magnetic field pulse with a magnetization direction 132 is generatedon the first ferromagnetic layer 112. Depending on the polarity of theapplied current pulse, the generated magnetic field switches the freelayer direction 132 to have a component that is positively or negativelyaligned to the reference magnetization direction 134 of the secondferromagnetic layer. FIG. 10A shows a generally positively alignedmagnetization direction 132 in the first ferromagnetic layer 112, andFIG. 10B shows a generally negatively aligned magnetization direction132 in the first ferromagnetic layer 112.

FIGS. 11A and 11B depict exemplary diagrams of bridge circuits formeasurement of a Z-axis of a magnetic field, with current linesenergized, according to various embodiments of the inventions. FIGS. 11Aand 11B show two exemplary Z-axis bridge configurations, with differentsense element magnetizations. It is understood that the flux guides 118shown in FIGS. 11A and 11B are only for a general illustration purpose.It is referred to as a collection of the flux guides within each Z-axisTMR transducer leg 310. Each Z-axis TMR transducer lea 310 a, 310 b, 310c, and 310 d may also have different magnetizations other than thepattern shown in FIGS. 11A and 11B.

FIG. 12 depicts an exemplary structure diagram of an array of X/Y-axisTMR element cells according to various embodiments of the inventions.The reset line 410 has a 45 degree cross angle to the firstferromagnetic layers 112. Such a reset line routing will have arelatively lower switching threshold and only need half of a resetcurrent to switch the magnetization directions of the firstferromagnetic layers 112 as compared to a 90 degree reset line routing.In one embodiment, four sense element cells may share a common referencelayer (MMT) for balanced sense current flow, whereby each TMR elementcell has equal SNR weighting. The element cells are electricallyconnected via a horizontal link (e.g., the first conductive line 124shown in FIGS. 5 and 7). Each horizontal link 124 couples a pair withina row of elements to a pair in the adjacent row.

FIG. 13 shows a second exemplary structure diagram of an array ofX/Y-axis TMR element cells according to various embodiments of theinventions. The reset line 410 has a 90 degree cross angle to the firstferromagnetic layers 112. The 90 degree reset line routing pattern needsa relatively higher reset current threshold to switch a magnetizationdirection of the first ferromagnetic layers 112 compared to the 45degree reset line routing pattern, but in some configurations, the 90degree reset line routing pattern is more robust. The 90 degree resetline routing pattern may be used for applications with a relativelyhigher power budget for the TMR sensor.

FIG. 14 shows an exemplary structure diagram of an array of Z-axis TMRelement cells according to various embodiments of the inventions. Dualflux guides trenches 118 a and 118 b are used for optimal trench widthwhile maintaining TJ pitch and spacing constraints. In one embodiment, asingle wide flux guide 118 c (not shown) may also be used instead of theconfiguration of dual flux guide trenches 118 a and 118 b. Similar toFIG. 8B, the Z-axis TMR element cells on each row are electricallyconnected via a horizontal link 124 through a sense element (i.e., firstferromagnetic layer 112) to a second ferromagnetic layer 114 (MMT),which may be connected in a desired pattern to construct the final TMRsensor. In one embodiment, a row 1030 of Z-axis TMR element cells havean opposite response to an out-of-plane field (Z-axis field) as comparedto a neighboring row 1040 of Z-axis TMR element cells. For example, theTMR element cells of row 1030 may have an increasing resistanceresponse, but the TMR element cells of row 1040 may have a decreasingresistance response. Therefore, the TMR element cells of the same rowmay be bundled together and act as a bridge leg (310) or a part of abridge leg for the bridge circuit 220 (shown in FIG. 9).

FIGS. 15A-15C depict exemplary schematic diagrams of an array of Z-axisTMR element cells according to various embodiments of the inventions.FIG. 15A shows a Wheatstone bridge circuit 1100 with each bridge leg1110, 1120, 1130, and 1140 representing a row (or multiple rows) ofZ-axis TMR element cells. The Wheatstone bridge circuit 1100 is coupledbetween a voltage source Vdd and a ground GND with diagonal bridge legshaving a same response to an out-of-plane field (Z-axis field). Thevoltage difference between the middle points m1 and m2 is the output ofthe Wheatstone bridge circuit 1100. The Wheatstone bridge circuit 1100may be constructed of different TMR element cell interleaving patterns.FIG. 15B shows a parallel interleaving pattern, and FIG. 15C shows aparallel interleaving pattern of longer serpentine paths for optimaltotal transducer resistance.

In FIG. 15B, each bridge leg corresponds to a row or parallel groupingof rows of TMR element cells disclosed in FIGS. 11A and 11B. The firstleg 1110 and third leg 1130 form one path between the voltage source Vddand ground GND. The second leg 1120 and fourth leg 1140 form anotherpath between the voltage source Vdd and ground GND. Each bridge legcorresponds to a row of TMR element cells. The first leg 1110 and thirdleg 1130 have opposite responses to an out-of-plane field (Z-axisfield). The second leg 1120 and fourth leg 1140 have opposite responsesto an out-of-plane field (Z-axis field). Moreover, the first leg 1110and second leg 1120 have opposite responses to an out-of-plane field(Z-axis field). The interleaving pattern is designed to ensure a maximumoutput between the between the middle points m1 and m2, and a densespatial fill without subtractive effects from adjacent sense elementcells and flux guides outlined previously. In one embodiment, a TMRmagnetic field sensor may comprise multiple such interleaving patternscoupled in parallel between the voltage source and ground.

In FIG. 15C, each bridge leg corresponds to multiple rows of TMR elementcells in series connection and the number of rows included within eachbridge leg is the same. Moreover, the TMR element cells within eachbridge leg have the same response to a Z-axis magnetic field. Similar toFIG. 15B, the four bridge legs 1110-1140 establish the Wheatstone bridgecircuit 1100 to ensure a maximum output between the between the middlepoints m1 and m2. Although each bridge leg consists of three rows of TMRelement cells, as shown in FIG. 15C, it is understood that the bridgeleg may consist of any desired odd number rows of TMR element cells. Ina preferred embodiment, the bridge leg may comprise rows of TMR elementcells for a bridge circuit output resistance in the order of 10 kΩ inorder to balance power consumption and Johnson noise.

FIG. 16 depicts an exemplary schematic diagram of an array of Z-axis TMRelement cells with 45 degree reset current lines according to variousembodiments of the inventions. The reset line 410 has a 45 degree crossangle to the first ferromagnetic layers 112. A 90 degree reset linerouting pattern needs a relatively higher reset current threshold toswitch a magnetization direction of the first ferromagnetic layers 112compared to the 45 degree reset line routing pattern. However, the 90degree reset line routing pattern is more robust for someconfigurations. The 90 degree reset line routing pattern may be used forapplications with a relatively higher power budget for the TMR sensor.

One skilled in the art will recognize that various implementations maybe realized within the described architecture, all of which fall withinthe scope of the inventions. For example, various reset current linerouting and/or energizing methods may be implemented in the TMR magneticfield sensors. For example, a bipolar reset current may be applied tothe reset current line to lower 1/f noise of the magnetic sensor. Thebipolar reset current may be applied in addition to the reset currentline routing patterns disclosed in the aforementioned embodiments.Moreover, the reset current line routing patterns may not be limited tothe aforementioned illustrated embodiments.

The foregoing description of the inventions has been described forpurposes of clarity and understanding. It is not intended to limit theinventions to the precise form disclosed. Various modifications may bepossible within the scope and equivalence of the application.

What is claimed is:
 1. A magnetic field sensor, comprising: a plurality of magnetoresistance sense elements coupled together as a first circuit to sense a magnetic field, wherein each magnetoresistance sense element of the plurality of magnetoresistance sense elements includes a first ferromagnetic layer and a second ferromagnetic layer separated by an insulating barrier layer; and a conductive line coupled to the first ferromagnetic layer of first and second magnetoresistance sense elements of the plurality of magnetoresistance sense elements, wherein the first magnetoresistance sense element and a third magnetoresistance sense element of the plurality of magnetoresistance sense elements share a common second ferromagnetic layer.
 2. The magnetic field sensor of claim 1, further comprising: at least one flux guide located between the first and second magnetoresistance sense elements.
 3. The magnetic field sensor of claim 1, wherein the at least one flux guide includes a plurality of flux guides.
 4. The magnetic field sensor of claim 2, wherein the at least one flux guide includes a thin ferromagnetic material layer on both sides of the at least one flux guide.
 5. The magnetic field sensor of claim 1, wherein, when a magnetic field is sensed by the plurality of magnetoresistance sense elements, a sense current flows through the first ferromagnetic layer, insulating barrier layer, and the second ferromagnetic layer of a magnetoresistance sense element, and wherein a direction of the sense current flow is perpendicular to the conductive line.
 6. The magnetic field sensor of claim 2, wherein the at least one flux guide is located symmetrically between the first and second magnetoresistance sense elements.
 7. The magnetic field sensor of claim 3, wherein the plurality of flux guides is located symmetrically between the first and second magnetoresistance sense elements.
 8. The magnetic field sensor of claim 6, wherein a width of the at least one flux guide covers a whole width between the first and second magnetoresistance sense elements.
 9. The magnetic field sensor of claim 2, wherein the at least one flux guide is located relatively closer to the first magnetoresistance sense element.
 10. The magnetic field sensor of claim 2, wherein the at least one flux guide is located above or below the first and second magnetoresistance sense elements.
 11. The magnetic field sensor of claim 3, wherein the plurality of flux guides are located above or below the first and second magnetoresistance sense elements.
 12. The magnetic field sensor of claim 3, wherein at least one flux guide of the plurality of flux guides includes a high permeability magnetic material.
 13. The magnetic field sensor of claim 1, wherein the first ferromagnetic layer of each magnetoresistance sense element includes a magnetization direction free to rotate in a magnetic field, and wherein the second ferromagnetic layer of each magnetoresistance sense element includes a fixed magnetization direction.
 14. The magnetic field sensor of claim 1, wherein the plurality of magnetoresistance sense elements includes one or more tunneling magnetoresistance sense elements, giant magnetoresistance sense elements, and/or anisotropic magnetoresistance sense elements.
 15. The magnetic field sensor of claim 1, further comprising: a second circuit comprising a plurality of current lines, wherein each current line of the plurality of current lines is adjacent to a corresponding magnetoresistance sense element of the plurality of magnetoresistance sense elements.
 16. The magnetic field sensor of claim 15, wherein at least one current line of the plurality of current lines is positioned above or below a magnetoresistance sense element.
 17. The magnetic field sensor of claim 15, wherein at least one current line of the plurality of current lines is positioned at a 45 degree cross angle relative to a first ferromagnetic layer of a magnetoresistance sense element of the plurality of magnetoresistance sense elements.
 18. The magnetic field sensor of claim 15, wherein at least one current line of the plurality of current lines is positioned at a 90 degree cross angle relative to a first ferromagnetic layer of a magnetoresistance sense element of the plurality of magnetoresistance sense elements.
 19. The magnetic field sensor of claim 10, wherein the at least one flux guide includes a first flux guide and a second flux guide, wherein the first flux guide is located above the first and second magnetoresistance sense elements, and wherein the second flux guide is located below the first and second magnetoresistance sense elements.
 20. A magnetic field sensor, comprising: a plurality of magnetoresistance sense elements coupled together as a first circuit to sense a magnetic field, wherein the plurality of magnetoresistance sense elements includes a first magnetoresistance sense element and a second magnetoresistance sense element located in a plane; and a plurality of flux guides, wherein a first flux guide of the plurality of flux guides is located above or below the first magnetoresistance sense element, and wherein the first flux guide is positioned between the first and second magnetoresistance sense elements, wherein each flux guide of the plurality of flux guides is configured to direct a portion of a magnetic field oriented orthogonally to the plane of first and second magnetoresistance sense elements into the plane of the first and second magnetoresistance sense elements, and wherein the first flux guide is configured to direct the magnetic field into the plane in a first direction, and a second flux guide of the plurality of flux guides is configured to direct the magnetic field into the plane in a second direction opposite the first direction. 